Field of the Invention
The present invention relates to an imaging device and a method of manufacturing the same, and for example, can suitably be made use of for an imaging device including a photodiode and an electrode pad.
Description of the Background Art
For example, an imaging device including a complementary metal oxide semiconductor (CMOS) image sensor is applied to a digital camera. In the imaging device, a photodiode is formed for converting incident light into charges. Charges generated in the photodiode are transferred to a floating diffusion region by a transfer transistor. The transferred charges are converted to an electric signal by an amplification transistor and output as an image signal.
A method of receiving incident light on a front surface of a semiconductor substrate has conventionally been known as a method of receiving incident light on a photodiode. A CMOS image sensor of this type is called a front side illuminated CMOS image sensor. In the front side illuminated CMOS image sensor, however, with reduction in size of the imaging device, incident light is cut off by multilayered interconnections formed on the photodiode and light incident on the photodiode has disadvantageously been weakened.
In order to solve this problem, for example, Patent Literature 1 (Japanese Patent Laying-Open No. 2011-14674) and Patent Literature 2 (Japanese Patent Laying-Open No. 2005-150463) have proposed a back side illuminated CMOS image sensor in which light is incident on a back surface of a semiconductor substrate opposite to a front surface on a side where interconnections are formed. Namely, a technique to receive incident light on a back surface of a semiconductor substrate decreased in thickness through polishing and to guide light to a photodiode formed on a front surface side of the semiconductor substrate has been proposed.
In such an imaging device having a back side illuminated CMOS sensor, since incident light is received on the back surface of the semiconductor substrate, an electrode pad for external electric connection is formed on the back surface of the semiconductor substrate and a metal wire is wire-bonded to the electrode pad. The electrode pad formed on the back surface of the semiconductor substrate and the interconnection formed on the front surface side of the semiconductor substrate are electrically connected to each other by a conductor passing through the semiconductor substrate. The conventional back side illuminated imaging device is constructed as above.